When multi-workpiece processing is carried out, i.e., a plurality of workpieces are mounted to a table of a machine tool and are successively machined, a rotation indexing table provided with a prism-shaped multi-face angle rest is generally utilized. Workpieces are mounted to respective workpiece mounting faces of angle rest, and after machining of one workpiece has finished, the table is indexed to proceed to machining of the next workpiece. As an example, a three face angle rest is disclosed in Japanese Unexamined Patent Publication No. 2004-142046.
Also, in Japanese unexamined Patent Publication No. 2001-225235, a machine tool is disclosed in which a main spindle is inclined to the vertical axis, and a turntable having a first table surface forming a machining area and a second table surface located outside the machining area so as to form workpiece setting and product pickup area is arranged for rotation on an axis of rotation situated in the midst of both surfaces, wherein the first table surface is arranged in a plane perpendicular to the inclined main spindle and the second table surface is arranged in a horizontal plane. This turntable is used such that workpieces are respectively mounted on the two surfaces inclined relative to each other in order to exchange workpieces between the workpiece machining area and the workpiece setting and pickup area.
In a case where multi-workpiece processing of a plurality of workpieces is performed using a five-axis numerically controlled machine tool having three linear feed axes for relatively moving a main spindle for mounting a tool relative to a table for mounting workpieces in three orthogonal directions of X, Y and Z axes and two orthogonal rotation feed axes for rotating the table about the linear feed axes. If a prism-shaped multi-face angle rest as disclosed in Japanese Unexamined Patent Publication No. 2004-142046 is used in this case, it is difficult to machine the lower surface of the workpiece facing to the upper surface of the table due to interference of the main spindle and the table. However, if multi-workpiece processing is to be performed without using a multi-face angle rest such that a plurality of workpieces are mounted in the same plane as the upper surface of the table, it is difficult to machine a surface of the workpiece facing to other workpiece due to interference of the main spindle with the workpieces.
In the case of the machine tool disclosed in Japanese Unexamined Patent Publication No. 2001-225235, so-called multi-workpiece machining in which the table is indexed only in the machining area and a plurality of workpieces are successively machined is not performed. Therefore, there is no description or suggestion of machining a plurality of workpieces without resulting in interference of the workpiece or table with the main spindle.